In a conventional flat knitting machine a sinker between knitting needles is employed to control a yarn threaded through a knitting needle in loop releasing, loop coupling, loop escaping and loop forming processes. The sinker has a protrusive edge at one side corresponding to the knitting needle head. When the sinker is rotated the protrusive edge presses the yarn picked up by the knitting needle to form a loop, thereby to form a pattern on the surface of the knitting fabric.
To control rotation of the sinker a control portion is provided at one side of the sinker in the flat knitting machine. For instance, U.S. Pat. No. 5,475,990 discloses a sinker control actuator which includes a first cam and a second cam positioned next to each other. The first and second cams are braced respectively by a first parallel bar and second parallel bar on a mounting rod. The cams are linked via an auxiliary bar. The first parallel bar, second parallel bar and auxiliary bar are linked in movements to control motions of the first and second cams, thereby to push the sinker on the first and second cams to change the rotation angle to form different sizes of loops. Reference of other linked movement structures can also be found in R.O.C. patent TW 446016, China patent publication No. 201288244 and China patent CN1544739.
The conventional first cam and second cam is swung by a switching member linked thereon. The switching member switches positions via a friction force or magnetic force with a needle bed, thereby drives the first and second cams swinging. The distance between the switching member and needle bed is constant. Hence flatness of the needle bed is important. Too great of the distance makes switching impossible, and too small of the distance increases the friction force between the switching member and needle bed that could latch the switching member on the needle bed.